Electronic/electrical devices have been reduced in weight, size, and thickness along with the recent development of electronic technology. In particular, a camera unit that is incorporated in a mobile phone and the like has been reduced in thickness and size, and required to exhibit improved F-number characteristics and modulation transfer function (MTF) characteristics. Therefore, an optical lens that is used for such a camera unit has been required to have a reduced thickness and a complex shape. Accordingly, such an optical lens has been designed to have a non-uniform thickness (i.e., have a thin part and a thick part) instead of a uniform thickness.
It has been desired to produce such an optical lens using an injection molding method that can reduce the production cost and is suitable for mass production. A lens having a diameter of less than 1 cm normally has a large optically effective area. However, it is difficult to increase the optically effective area when producing a lens by injection molding since a weld line occurs, or birefringence becomes non-uniform.
Patent Document 1 discloses a method that produces a small and thin lens by injection molding using a composition that includes a norbornene-based polymer and wax. In this case, however, the wax may bleed out from the surface of the resulting formed article (lens), and contaminate the mold, for example. Patent Document 2 discloses that a polymer that has a specific monomer composition exhibits an excellent thin article-forming capability, and produces a small and thin lens that exhibits optical properties and heat resistance in a well-balanced manner.
Patent Document 3 discloses that a polymer (norbornene-based ring-opening copolymer) obtained by subjecting a norbornene-based monomer to ring-opening polymerization in the presence of a linear α-olefin having 14 to 40 carbon atoms produces a film that exhibits water vapor barrier properties, transparency, and heat resistance in a well-balanced manner, and is suitable as a packaging material or an electronic device-sealing material.